Toner, method for manufacturing same, and imaging apparatus using same

Abstract: The present invention aims to provide a deformed toner having a narrow toner particle size distribution, a simple manufacturing method of same, and an imaging apparatus using same. The toner particles have an average diameter of d (d is in a range of 4-15 µm), and a volumetric fraction of the particles have a diameter in the range of d ± 0.2d equals to or exceeds 90 % of total volume of the particles, and further, when a specific surface area of the toner per 1 cm³ determined by a BET method is expressed by A (m²/g) and a specific gravity of the particle is expressed by D (g/cm³), A of the particles stands in a range expressed by an equation, 7/(D·d) ≦ A ≦ 10/(D·d) . An image having a preferable definition can be obtained by improving a resolution of image by making the particle size distribution of toner particles narrow, and providing the toner having an electrification charge at least 10 µC/g with a narrow distribution.

Description: Background of the Invention (1) Field of the Invention: The present invention relates to an electrophotographic toner having a deformed spherical shape of substantially a same particle size, an easy method for obtaining same, and the use of the resulting toner particles in an electrophotographic developing apparatus. The term "deformed" here means "processed for having a shape of other than a substantially exact sphere", and the same hereinafter. (2) Description of the Prior Art: Solid ink called toner is widely used in image forming methods such as electronic photograph, and electrostatic recording method etc. As for a general method for manufacturing the toner, a method has been used in which resin and additives such as coloring agents are mixed together, the mixture is pulverized into particles having small diameters, and subsequently the particles are classified in order to obtain particles having adequate diameters. Currently, so-called polymerized toner capable of being manufactured without the pulverization and the classification has widely been studied (JP-A-57-154253 (1982)). The polymerized toner is manufactured without the pulverizing operation after polymerization of the resin by controlling a particle size distribution to an adequate one for toner particles when the resin is produced by a suspension polymerization method or an emulsion polymerization method. The toner particles obtained by the above methods have a narrower particle size distribution than that of the particles obtained by the pulverization method, and accordingly, the classification of the particles is not necessary. Further, the toner particle obtained by the above method has a smaller surface area than that of the toner particle obtained by the prior art, and accordingly, the toner particle has an advantage of being small hygroscopic. When the toner is manufactured by a polymerization method, the process has the steps of polymerizing the resin, settling the particles by centrifuging, removing dispersing agents by repeating the settling and decanting after adding water to the particles, and drying the particles. The above described process is complex in its operation, and is more disadvantageous in necessary time and cost than the conventional pulverization method. Further, the particles obtained by the polymerization method have a problem that the particle is substantially an exact spherical shape, although the particles have a relatively same diameter. When the particle is an exact sphere, the particle has a small surface area, and has had a problem for being used as a toner such as a poor charging property because of a very small contacting area with a developing object, e.g. a drum and paper, at a developing operation. According to documents EP-A-0 445 986 and GB-A-2 258 053 toner particles with specific properties, such as volume-average particle diameter, shape factor, BET specific surface area, can be prepared by a suspension polymerization process, the toner particles being substantially spherical. Also Patent Abstract of Japan JP-A-59058438 discloses spherical toner particles having specifically restricted physical values obtained by a polymerisation method. In order to overcome the above described problem, a several methods for deforming the particles are studied. For example, a method wherein a fine particle obtained by another polymerization method is attached to the particle obtained by the above polymerization method (JP-A-1-10263 (1989)), and methods for obtaining deformed particles by pulverizing the particles obtained by the polymerization method with giving physical impact by a ball milling and so on have been proposed. However, all of the example methods have a problem that the toner particles having substantially a same diameter are very difficult to be obtained without the classification because the attached fine particle in the former case and generated fine particles by the ball milling in the latter cases expand a width of their particle diameter distribution. Summary of the Invention (1) Object of the Invention: Object of the present invention is to provide a toner having a deformed spherical shape of substantially a same particle size, an easy method for obtaining same, and the use of said toner particles in an electrophotographic developing apparatus. (2) Methods Solving the Problems: In order to realize the above described object of the present invention, the following means are effective; The first means are toner particles having an average diameter d in the range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, and further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by the equation: 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ). The second means are toner particles having an average diameter d in a range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by the equation 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ), and the particles have surface irregularities of utmost 2 µm in depth. The third means are toner particles having an average diameter d in the range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by the equation, 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ), and the particles have a ratio (a)/(b) which is less than 2 where (a) is the major axis and (b) is the minor axis of the toner particles respectively. The fourth means are toner particles having an average diameter d in the range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by the equation, 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ), and the particles have an electrical chargeability of at least 10 µC/g (determined with a blow off charged electricity measuring apparatus). The fifth means are toner particles having an average diameter d in the range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by an equation, 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ), and the volumetric fraction of the particles having a specific surface area A expressed by the equation, 6/(D•d) ≤ A < 7/(D•d), is equal to or less than 10 % of the total volume of the particles. The sixth means are toner particles having an average diameter d is in a range of 4-15 µm characterized in that the volumetric fraction of the particles having a diameter in the range of d ± 0.2d is equal to or higher than 90 % of the total volume of the particles, further, the specific surface area A(m 2 /g) determined by the BET method is in the range expressed by the equation, 7/(D•d) ≤ A ≤ 10/(D•d), wherein D is the density of the particles (g/cm 3 ), and the toner particles are polymers obtained by polymerization reaction of at least one kind of monomers having at least an ester group. The seventh means is a method for manufacturing toner particles with deformed spherical shape, comprising the steps of; (a) providing polymerized toner particles comprising monomer units having a hydrolyzable group, (b) aggregating the particles in the polymerization system through hydrolysis by making the system alkaline, (c) separating the aggregates of the particles from the reaction system, (d) disintegrating the aggregates of the particles by acidifying the system, and (e) collecting the particles. The eighth means is a developing apparatus for forming a toner image by an electronic photograph system, wherein the toner particles according to the present invention are used. The ninth means is a developing apparatus for forming a toner image by an electronic photograph system, wherein the resolution MTF (modulation transfer function) is at least 0.5 with 500 dots/inch. The tenth means is a developing apparatus for forming a toner image by an electronic photograph system, wherein an enlarged image magnified by 10-1000 times of an original image is formed clearly. If the average diameter d of the toner particle is less than 4 µm in the present invention, it is not preferable because the toner particle has a possibility to cause silicosis when the particles are inhaled by mistake. And, if the average diameter d of the toner particle is larger than 15 µm, improvement of the resolution can not be realized. When the particle size distribution of the toner particles becomes larger than ± 0.2d, the distribution of the toner particle surface area becomes broader, and accordingly, the distribution of frictional electrification charges becomes wider. Consequently, the resolution of the image decreases. In accordance with the present invention, the resolution MTF (modulation transfer function) of the obtained image of at least 0.5 - 500 dots/inch can be achieved by making the particle size distribution such that the diameters of the particles occupying more than 90 % of the total sum of the particles' volume are in the range of d ± 0.2d, where d is the average diameter of the particles (d is in the range of 4-15 µm). The present invention improves the resolution of the image by making the particle size distribution of the toner particles narrow, and further, according to the present invention the toner has an enough surface area for ensuring sufficient electrical chargeability of more than 10 µC/g by deforming the substantially exact spherical shape of the polymer toner particle, and the invention makes it possible to charge very uniform and efficiently. Consequently, it becomes possible to realize a high definition image which has not been obtained. Moreover, electrical chargeability of more than 10 µC/g and making the distribution of the amount of the charged electricity very narrow and uniform can be controlled efficiently by realizing the feature of the present invention, i.e. the toner particle has a deformed spherical shape, the toner particle has irregularities of utmost 2 µm deep on its surface, and the toner particle has a ratio of (a)/(b) less than 2 where (a) is a major axis and (b) is a minor axis of the toner particle, respectively. The degree of the deformation of the toner particles can be determined by a specific surface area measurement of the particles. The specific surface area of the particles is usually determined by the BET method. Here, a specific surface area per 1 gram of the toner is indicated as A (m 2 /g). If the toner is composed of exact spherical particles, the A becomes about 6/(D•d). The toner manufactured by the polymerization method has an A of about 6/(D•d) to 7/(D•d). However, it is difficult to control the electrification charge of the above polymerized toner, because the shapes of the toner particles are too similar with exact spheres. On the contrary, if the A of the polymerized toner exceeds 10/(D•d), the toner particles are too deformed to have a narrow particle size distribution, and the toner particles may have a disadvantage of a large hygroscopic property. Generally, the toner obtained by the conventional pulverizing method has an A of about 11/(D•d) to 18/(D•d). The toner having a deformed spherical shape and the above described particle size distribution of d ± 0.2d (d is in a range 4-15 µm) can be obtained, for example, by the following method. First, polymers are obtained by polymerization reaction in a solution of monomers having an ester group with predetermined blending components (a suspension polymerization is preferable). Diameters of the polymer particles are optionally adjustable depending on components, temperature, and time of the polymerization reaction. Subsequently, the reacted solution is made alkaline after the polymerization reaction has been completed (this operation is called "alkaline treatment" hereinafter). The alkaline treatment is for hydrolysis of the ester group in the polymer. Consequently, the ester group is converted to carboxylic acid salt as shown in FIG. 1, and the polymer becomes hydrophilic.As a result, the surface of the particle absorbs water somewhat, and the particles aggregate each other to form a block having a diameter of a few millimeters. When the particles form a block of such size, filtration with a filter paper becomes possible (with the particle size before the above aggregation, clogging of pores in the filter paper occurs easily). After the filtration, washing with water is repeated in order to remove water soluble components such as dispersing agents. Next, the obtained block is mixed with an acidic liquid, and the mixture is agitated vigorously (this operation is called "acid treatment" hereinafter) to separate the block into particles having the same diameter as that of the particle of soon after the polymerization by converting the carboxylic acid salt to the carboxylic acid. Because the obtained particle hardly disperses in water, but mainly precipitates, supernatant liquid can easily be removed by decantation without centrifuging operation. The particle obtained after the decantation has a deformed shape with irregularities such as collapses and dimples at the surface. The above described changes of the particle by the alkali treatment and the acid treatment are schematically indicated in FIG. 2. An example of prior art in which an alkali treatment is performed after polymerization is indicated in JP-A-3-113464 (1991). However, the alkali treatment in the prior art differs substantially from the alkali treatment of the present invention, because, in the prior art, monomers having carboxylic acid group are used for the polymerization and an aim of the alkali treatment is to control pH at a level that the carboxylic acid does not generate a salt (pH 4-7). As for an agent used in making the reacted solution alkaline after the polymerization reaction, alkali metal hydroxides or alkali earth metal hydroxides both of which have large solubilities in water are preferable. Concretely saying, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali earth metal hydroxides such as magnesium hydroxide and calcium hydroxide are preferable. However, some metallic hydroxides which are scarcely soluble in water can not be thought suitable because of their difficulty in removing by washing with water. Ammonia water is also preferable because of large solubility in water. Ammonia gas also has an advantage not to increase an amount of the reacted solution so much. However, ammonia gas is poisonous and sufficient caution is required in handling for the gas leak from its vessel etc. Preferable acidic liquids used in the operation for separating the block into particles by the acid treatment are such as aqueous solution of hydrochloric acid, nitric acid, or sulfuric acid. Aqueous solutions of the above described acids can convert carboxylic acid salts to corresponding carboxylic acids without any side reaction if their concentration is not extremely high (about 0.01-5 % by weight). When organic acids such as acetic acid are used, there is an possibility to cause swelling or dissolving of the particle depending on kinds of the resin forming the particle, and sufficient caution is required. Preferable monomers having an ester group contained in the monomers for the resin are such as alkyl methacrylates, alkyl acrylates, or vinyl acetates etc. Among them, alkyl methacrylates, or alkyl acrylates is superior to others in transparency. In case the flexibility of the ink after development is required, alkyl methacrylates, or alkyl acrylates having a relatively long alkyl chain (concretely saying, the number of carbon atoms in the alkyl chain is four or more) are advantageous. In case heat resistance of the ink is required, alkyl methacrylates, or alkyl acrylates having a relatively short alkyl chain (concretely saying, the number of carbon atoms in the alkyl chain is three or less) are advantageous. When at least 70 % by weight monomers having an ester group are contained in the monomers for the resin, there may be a case in which a fairly large fraction of the particles dissolve into water a the alkali treatment. Accordingly, the monomer having an ester group is preferably contained in the monomers for the resin in a range from 5 % by weight to 70 % by weight. As for the monomer having an ester group in the present invention, alkyl methacrylates, or alkyl acrylates having carbon atoms in the range from 1 to 9 are advantageous in obtaining the polymer toner relating to the present invention. That is, the above described compounds facilitate to obtain the toner having a narrow particle size distribution such as d ± 0.2d and a deformed spherical shape by suspension polymerization. In the present invention, monomers having any group which can be hydrolyzed such as amido group, or imido group in addition to the ester group can be used as starting material for the polymer, and further, the above described monomers can be used with the monomer having an ester group for copolymerization reaction. Additives such as coloring agents, or charge control agents are added to the manufactured toner. Generally, these additives are added to the monomer at the polymerization reaction, but some additives can be added to the toner at the treatment after the polymerization reaction depending on the cases. For example, almost of charge control agents of amine group can be adsorbed by carboxyl groups at the surface of the particle after the acid treatment. The imaging apparatus can reproduce information contained in a microfilm and the like as a readable magnified image by magnifying to several times or more from 10 to 1000 times depending on kinds of data with a combination of a plurality of lenses in an optical system of the apparatus. As for developing methods using the toner of the present invention, either of a double components method using a carrier for charging the toner and a single component method using a brush and so on other than a carrier for charging the toner are applicable. The aggregation of the particles after the polymerization reaction is assumed to be caused by changing the surface condition of the particles with a carboxylic acid salt generated by hydrolysis of the ester group in the particle. Further, the reason why the particles scarcely disperse in an acidic liquid is assumed because of the removal of a dispersant in the particles by the alkali treatment. The reason why the particle obtained by the acid treatment has irregularities on its surface is assumed because of a process in which water is impregnated into the particle from its surface which has been changed to be water soluble by the hydrolysis of the ester group to make the particle swelled, and subsequently, the impregnated water is released from the particle outside by the acid treatment which decreases water solubility of the particle, or because of deformation caused by compressing surfaces of the particles each other when the particles aggregate by the alkali treatment. Further, the aggregating force of the particles at the aggregation process is extremely weaker than that of the particles which have been heated beyond its glass transition temperature (Tg) to weld each other, and accordingly, the aggregate easily reduces its size to the same size as the particle before the aggregation by only agitating the liquid after the acidic treatment with an over-head stirrer. Moreover, because the agitating operation with the over-head stirrer has a weaker mechanical impacting force than that of a ball milling operation, excessively pulverized particles are scarcely generated, and accordingly, the particles having substantially the same diameter can be obtained. When the shape of the toner particle obtained by the polymerization process is exactly spherical, it is very difficult to give a sufficient charge to the toner which is deformed by a conventional pulverizing method even if an electrification controlling agent is added to the toner. Brief Description of the Drawings FIG. 1 is a schematic illustration for indicating changes of an ester group in the resin at the particle surface by the treatments of the present invention, FIG. 2 is a schematic illustration for indicating changes in shapes of the particle by the treatment of the present invention, FIG. 3 is a schematic illustration for an imaging apparatus using the toner of the present invention, FIG. 4 is a schematic illustration for an optical system of the imaging apparatus using the toner of the present invention. Detailed Description of the Embodiments Embodiment 1 Polymerized tcner particles were prepared by the following procedure. Polyvinyl alcohol (1 part by weight) was dissolved into warm distilled water (10 parts by weight). Subsequently, carbon black (MA-8 made by Mitsubishi Chemicals) (10 parts by weight), a charge control agent (Bontron N-03 made by Orient Chemicals) (5 parts by weight), were added to the solution, and a paste was prepared by grinding the mixture well in a mortar. Then, the whole amount of the paste was mixed with the following reagents and agitated for 4 hours at 60 °C under a nitrogen atmosphere. Methyl methacrylate 50 parts by weight Stylene 200 parts by weight Polyvinyl alcohol 1 part by weight Potassium persulfate 1 parts by weight Distilled water 1000 parts by weight As a result, a reacted solution in which polymerized particles having a diameter of approximately 10 µm had been dispersed was obtained. After the above polymerization reaction was completed, the reacted solution was added with sodium hydroxide, 10 parts by weight, and the polymerized particles were aggregated by agitating the reacted solution for one minute at 60 °C. The reacted solution was filtered with a filter paper (Toyo paper filter No. 2). The obtained solid was washed a several times with water, added into 1 % by weight hydrochloric aqueous solution, 1000 part by weight, and agitated at 60 °C. As agitating, the aggregate reduced its size by disintegration, and the polymerized particles precipitated at the bottom of the vessel by standing the solution still after the agitation until the temperature of the solution lowered to a room temperature. After removing the supernatant solution by decantation, the same amount of water as the supernatant was added to the precipitate, agitated the mixture for a while, stood the mixture still, and decanted. Subsequently, ethyl alcohol 1 part by weight was added, the mixture was agitated, and then the mixture was poured into a vat made from a metal and left for two days at room temperature to dry it. Finally, toner particles having a diameter of approximately 10 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Observation of the obtained toner particle with a microscope revealed that the particle had the shape of a flatten sphere. Maximum length of major axises of almost particles (more than 90 %) were less than two times of the minimum length of minor axises each of which was across the major axis at the middle of the axis. Determination of a particle size distribution (volumetric distribution) of the particles by a Coulter counter (Model TAII made by Coulter Co. ) revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in the range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the BET method to be 0.8 m 2 /g which satisfied the above range. The apparatus used in the above determination was a betasorb automatic surface area measuring apparatus model 4200 made by Nikiso Co. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 25 µC/g with 5 minutes agitation. The above value equals to an amount of electrification obtained with a toner which was prepared by a conventional pulverizing method. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron N-03 in the manufacturing process was determined in the same manner to be 4 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron N-03 and the other case which did not use Bontron N-03 was 21 µC/g. FIG. 3 indicates a schematic illustration of an imaging apparatus using the toner prepared by the method of the present invention. With using the apparatus, clear images having at least 0.5 of MTF at 600 dpi are obtainable. As for developing methods using the toner obtained in the present embodiment, either of a double components method using a carrier for charging the toner and a single component method using a brush and so on other than a carrier for charging the toner are applicable. FIG. 4 indicates a schematic illustration of an optical system used in the above imaging apparatus. A the optical system, and a distance between the lenses, the numbers and kinds of the lenses are controlled corresponding to a necessary magnification. As ordinary optical microscopes are capable of magnifying an objective to 1000 times, it is possible to obtain an image having a larger magnification than that obtained by a conventional one such as a few times, or more as 10 to 1000 times. Comparative example 1 A reacted solution in which polymerized particles having a diameter of approximately 10 µm had been dispersed was obtained in the same manner as the above embodiment 1. A filtrating procedure was attempted on the reacted solution without adding sodium hydroxide as performed in the embodiment 1 using the same filter paper as the one used in the embodiment 1. However, it was very difficult to obtain the polymerized particles because the filter paper was clogged soon after the procedure started. Subsequently, the reacted solution was centrifuged by 5000 rpm for 30 minutes, the supernatant liquid was discarded, the same amount of water as the discarded supernatant liquid was added to the precipitates, the mixture was agitated, and the mixture was centrifuged again. Subsequent to the above cycle repeated a several times, ethyl alcohol 1 part by weight was added to the precipitates after discarded the supernatant and agitated for mixing well. Then, the mixture was poured into a vat made from a metal, and left for two days at a room temperature to dry it. Finally, toner particles having a diameter of approximately 10 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Microscopic observation of the obtained toner particle revealed that the shape of the particle was exactly a sphere. Determination of a particle size distribution (weight distribution) of the particles by a Coulter counter (Model TAII made by Coulter Co.) revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the same method as the embodiment 1 to be 0.74 m 2 /g which did not satisfy the above range. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 8 µC/g with 5 minutes agitation. The amount of electrification was less than 10 µC/g even if agitated for 10 minutes. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron N-03 in the manufacturing process was determined in the same manner to be 2 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron N-03 and the other case which did not use Bontron N-03 was 6 µC/g. Embodiment 2 Using butyl acrylate (50 parts by weight) in place of methyl methacrylate (50 parts by weight) in the above embodiment 1, toner particles having a diameter of approximately 10 µm were obtained by the polymerization reaction and the post treatments in the same manner as the embodiment 1. In the post treatments, the toner particles after the alkali treatment aggregated as same as the embodiment 1, and the filtration procedure could be performed smoothly. Microscopic observation of the obtained particle revealed that the particle had the same shape as that of the particle in the embodiment 1. As explained above, even if the kind of the resin monomer was varied, the post treatment could be performed smoothly by the filtration procedure, and the obtained toner particle had a deformed shape. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 0.88 m 2 /g which satisfied the above range. Embodiment 3 After the polymerization reaction was performed in the same manner as the embodiment 1, the post treatments was processed in the same manner as the embodiment 1 except potassium hydroxide (10 parts by weight) was used in place of sodium hydroxide (10 parts by weight), and toner particles having a diameter of approximately 10 µm were obtained. In the post treatments, the toner particles after the alkali treatment aggregated as same as the embodiment 1, and the filtration procedure could be performed smoothly. Microscopic observation of the obtained particle revealed that the particle had the same shape as that of the particle in the embodiment 1. Further, a same result as the case using potassium hydroxide was obtained by using an ammonia water (25 % by weight, 40 parts by weight) in place of potassium hydroxide. As explained above, even if the kind of the reagent in the alkali treatment was varied, the post treatment could be performed smoothly by the filtration procedure, and the obtained toner particle had a deformed shape. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 0.81 m 2 /g which satisfied the above range. Embodiment 4 After the polymerization reaction and alkali treatment were performed in the same manner as the embodiment 1, the post treatments was processed in the same manner as the embodiment 1 except nitric acid (5 % by weight, 1000 parts by weight) was used in place of hydrochloric acid (5 % by weight, 1000 parts by weight) in the acid treatment, and toner particles having a diameter of approximately 10 µm were obtained. In the post treatments, the toner particles after the acid treatment disintegrated their aggregate and precipitated at the bottom of the vessel, and the subsequent procedure could be performed very smoothly as same as the embodiment 1. Microscopic observation of the obtained particle revealed that the particle had the same shape as that of the particle obtained in the embodiment 1. As explained above, even if the kind of the reagent in the acid treatment was varied, the post treatment could be performed smoothly by the filtration procedure, and the obtained toner particle had a deformed shape. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 0.81 m 2 /g which satisfied the above range. Embodiment 5 Polymerized toner particles were prepared by the following procedure. Polyvinyl alcohol (1 part by weight) was dissolved into warm distilled water (10 parts by weight). Subsequently, carbon black (MA-8 made by Mitsubishi Chemicals) (10 parts by weight), a charge control agent (Bontron N-34 made by Orient Chemicals) (5 parts by weight), were added to the solution, and a paste was prepared by grinding the mixture well in a mortar. Then, whole amount of the paste was mixed with the following reagents and agitated for 4 hours at 60 °C under a nitrogen atmosphere. Methyl methacrylate 50 parts by weight Stylene 200 parts by weight Polyvinyl alcohol 1 part by weight Potassium persulfate 1 parts by weight Distilled water 1000 parts by weight As a result, a reacted solution in which polymerized particles having a diameter of approximately 10 µm had been dispersed was obtained. After the above polymerization reaction was completed, the reacted solution was added with sodium hydroxide, 10 parts by weight, and agitated for one minute at 60 °C to aggregate the polymerized particles. The reacted solution was filtered with a filter paper (Toyo paper filter No. 2). The obtained solid was washed a several times with water, added into 1 % by weight hydrochloric aqueous solution, 1000 part by weight, and agitated at 60 °C. As agitating, the aggregate reduced its size by disintegration, and the polymerized particles precipitated at the bottom of the vessel by standing the solution still after the agitation until the temperature of the solution lowered to a room temperature. After removing the supernatant solution by decantation, the same amount of water as the supernatant was added to the precipitate, agitated the mixture for a while, stood the mixture still, and decanted. Subsequently, ethyl alcohol 1 part by weight was added to the precipitate, the mixture was agitated, and then the mixture was poured into a vat made from a metal and left for two days at a room temperature to dry it. Finally, toner particles having a diameter of approximately 10 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Observation of the obtained toner particle with a microscope revealed that the particle had a shape of a flatten sphere. Maximum length of major axises of almost particles (more than 90 %) were less than two times of minimum length of minor axises each of which was across the major axis at the middle of the axis. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 10 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 8-12 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.78 ≤ A ≤ 1.11. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 0.80 m 2 /g which satisfied the above range. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 22 µC/g with 5 minutes agitation. The above value equals to an amount of electrification obtained with a toner which was prepared by a conventional pulverizing method. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron S-34 in the manufacturing process was determined in the same manner to be 4 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron S-34 and the other case which did not use Bontron S-34 was 26 µC/g. FIG. 3 indicates a schematic illustration of an imaging apparatus using the toner prepared by the method of the present invention. With using the apparatus, clear images having at least 0.5 of MTF at 600 dpi are obtainable. FIG. 4 indicates a schematic illustration of an optical system used in the above imaging apparatus. A plurality of lenses are associated with each other in the optical system, and a distance between the lenses, the numbers and kinds of the lenses are controlled corresponding to a necessary magnification. As ordinary optical microscopes are capable of magnifying an objective to 1000 times, it is possible to obtain an image having a larger magnification than that obtained by a conventional one such as a few times, or more as 10 to 1000 times. Embodiment 6 Polymerized toner particles were prepared by the following procedure. Polyvinyl alcohol (1 part by weight) was dissolved into warm distilled water (10 parts by weight). Subsequently, carbon black (MA-8 made by Mitsubishi Chemicals) (10 parts by weight), a charge control agent (Bontron N-04 made by Orient Chemicals) (5 parts by weight), were added to the solution, and a paste was prepared by grinding the mixture well in a mortar. Then, whole amount of the paste was mixed with the following reagents and agitated for 4 hours at 60 °C under a nitrogen atmosphere. Methyl methacrylate 60 parts by weight Stylene 200 parts by weight Polyvinyl alcohol 1 part by weight Potassium persulfate 1 parts by weight Distilled water 1000 parts by weight As a result, a reacted solution in which polymerized particles having a diameter of approximately 11 µm had been dispersed was obtained. After the above polymerization reaction was completed, the reacted solution was added with sodium hydroxide, 10 parts by weight, and agitated for one minute at 60 °C to aggregate the polymerized particles. The reacted solution was filtered with a filter paper (Toyo paper filter No. 2). The obtained solid was washed a several times with water, added into 1 % by weight hydrochloric aqueous solution, 1000 part by weight, and agitated at 60 °C. As agitating, the aggregate reduced its size by disintegration, and the polymerized particles precipitated at the bottom of the vessel by standing the solution still after the agitation until the temperature of the solution lowered to a room temperature. After removing the supernatant solution by decantation, the same amount of water as the supernatant was added to the precipitate, agitated the mixture for a while, stood the mixture still, and decanted. Subsequently, ethyl alcohol 1 part by weight was added to the precipitate, the mixture was agitated, and then the mixture was poured into a vat made from a metal and left for two days at a room temperature to dry it. Finally, toner particles having a diameter of approximately 11 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Observation of the obtained toner particle with a microscope revealed that the particle had a shape of a flatten sphere. Maximum length of major axises of almost particles (more than 90 %) were less than two times of minimum length of minor axises each of which was across the major axis at the middle of the axis. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 11 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 9-13 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.71 ≤ A ≤ 1.01. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 0.74 m 2 /g which satisfied the above range. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 20 µC/g with 5 minutes agitation. The above value equals to an amount of electrification obtained with a toner which was prepared by a conventional pulverizing method. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron N-04 in the manufacturing process was determined in the same manner to be 4 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron N-04 and the other case which did not use Bontron N-04 was 16 µC/g. FIG. 3 indicates a schematic illustration of an imaging apparatus using the toner prepared by the method of the present invention. With using the apparatus, clear images having at least 0.5 of MTF at 600 dpi are obtainable. FIG. 4 indicates a schematic illustration of an optical system used in the above imaging apparatus. A plurality of lenses are associated with each other in the optical system, and a distance between the lenses, the numbers and kinds of the lenses are controlled corresponding to a necessary magnification. As ordinary optical microscopes are capable of magnifying an objective to 1000 times, it is possible to obtain an image having a larger magnification than that obtained by a conventional one such as a few times, or more as 10 to 1000 times. Embodiment 7 Polymerized toner particles were prepared by the following procedure. Polyvinyl alcohol (1 part by weight) was dissolved into warm distilled water (10 parts by weight). Subsequently, carbon black (MA-8 made by Mitsubishi Chemicals) (10 parts by weight), a charge control agent (Bontron N-03 made by Orient Chemicals) (5 parts by weight), were added to the solution, and a paste was prepared by grinding the mixture well in a mortar. Then, whole amount of the paste was mixed with the following reagents and agitated for 4 hours at 60 °C under a nitrogen atmosphere. Hexyl methacrylate 150 parts by weight Stylene 200 parts by weight Polyvinyl alcohol 20 part by weight Potassium persulfate 1 parts by weight Distilled water 1000 parts by weight As a result, a reacted solution in which polymerized particles having a diameter of approximately 5 µm had been dispersed was obtained. After the above polymerization reaction was completed, the reacted solution was added with sodium hydroxide, 10 parts by weight, and agitated for one minute at 60 °C to aggregate the polymerized particles. The reacted solution was filtered with a filter paper (Toyo paper filter No. 2). The obtained solid was washed a several times with water, added into 1 % by weight hydrochloric aqueous solution, 1000 part by weight, and agitated at 60 °C. As agitating, the aggregate reduced its size by disintegration, and the polymerized particles precipitated at the bottom of the vessel by standing the solution still after the agitation until the temperature of the solution lowered to a room temperature. After removing the supernatant solution by decantation, the same amount of water as the supernatant was added to the precipitate, agitated the mixture for a while, stood the mixture still, and decanted. Subsequently, ethyl alcohol 1 part by weight was added to the precipitate, the mixture was agitated, and then the mixture was poured into a vat made from a metal and left for two days at a room temperature to dry it. Finally, toner particles having a diameter of approximately 5 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Observation of the obtained toner particle with a microscope revealed that the particle had a shape of a flatten sphere. Maximum length of major axises of almost particles (more than 90 %) were less than two times of minimum length of minor axises each of which was across the major axis at the middle of the axis. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 5 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 4-6 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 1.56 ≤ A ≤ 2.22. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 1.69 m 2 /g which satisfied the above range. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 30 µC/g with 5 minutes agitation. The above value equals to an amount of electrification obtained with a toner which was prepared by a conventional pulverizing method. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron N-03 in the manufacturing process was determined in the same manner to be 5 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron N-03 and the other case which did not use Bontron N-03 was 25 µC/g. FIG. 3 indicates a schematic illustration of an imaging apparatus using the toner prepared by the method of the present invention. With using the apparatus, clear images having at least 0.5 of MTF at 600 dpi are obtainable. FIG. 4 indicates a schematic illustration of an optical system used in the above imaging apparatus. A plurality of lenses are associated with each other in the optical system, and a distance between the lenses, the numbers and kinds of the lenses are controlled corresponding to a necessary magnification. As ordinary optical microscopes are capable of magnifying an objective to 1000 times, it is possible to obtain an image having a larger magnification than that obtained by a conventional one such as a few times, or more as 10 to 1000 times. Embodiment 8 Polymerized toner particles were prepared by the following procedure. Polyvinyl alcohol (1 part by weight) was dissolved into warm distilled water (10 parts by weight). Subsequently, carbon black (MA-8 made by Mitsubishi Chemicals) (10 parts by weight), a charge control agent (Bontron N-03 made by Orient Chemicals) (5 parts by weight), were added to the solution, and a paste was prepared by grinding the mixture well in a mortar. Then, whole amount of the paste was mixed with the following reagents and agitated for 4 hours at 60 °C under a nitrogen atmosphere. Methyl methacrylate 25 parts by weight Butyl acrylate 25 parts by weight Stylene 200 parts by weight Polyvinyl alcohol 5 part by weight Potassium persulfate 1 parts by weight Distilled water 1000 parts by weight As a result, a reacted solution in which polymerized particles having a diameter of approximately 8 µm had been dispersed was obtained. After the above polymerization reaction was completed, the reacted solution was added with sodium hydroxide, 10 parts by weight, and agitated for one minute at 60 °C to aggregate the polymerized particles. The reacted solution was filtered with a filter paper (Toyo paper filter No. 2). The obtained solid was washed a several times with water, added into 1 % by weight hydrochloric aqueous solution, 1000 part by weight, and agitated at 60 °C. As agitating, the aggregate reduced its size by disintegration, and the polymerized particles precipitated at the bottom of the vessel by standing the solution still after the agitation until the temperature of the solution lowered to a room temperature. After removing the supernatant solution by decantation, the same amount of water as the supernatant was added to the precipitate, agitated the mixture for a while, stood the mixture still, and decanted. Subsequently, ethyl alcohol 1 part by weight was added to the precipitate, the mixture was agitated, and then the mixture was poured into a vat made from a metal and left for two days at a room temperature to dry it. Finally, toner particles having a diameter of approximately 8 µm were obtained by drying the particles for 3 hours at 60 °C in a drying oven. Observation of the obtained toner particle with a microscope revealed that the particle had a shape of a flatten sphere. Maximum length of major axises of almost particles (more than 90 %) were less than two times of minimum length of minor axises each of which was across the major axis at the middle of the axis. Determination of a particle size distribution of the particles by the same method as that of the embodiment 1 revealed that the maximal diameter of the particles was 8 µm and diameters of the particles occupying more than 90 % of total sum of the particles' volume stand in a range of 6.5-9.5 µm. The specific gravity of the toner was 0.90. Therefore, the specific surface area A which satisfies the equation 7/(D•d) ≤ A ≤ 10/(D•d) was in a range of 0.97 ≤ A ≤ 1.39. The specific surface area of the toner was determined by the same method as that of the embodiment 1 to be 1.08 m 2 /g which satisfied the above range. An amount of electrification of the obtained toner was determined by a blow-off electrification measuring apparatus (TB-200 made by Toshiba Chemicals Co.) to be 27 µC/g with 5 minutes agitation. The above value equals to an amount of electrification obtained with a toner which was prepared by a conventional pulverizing method. A carrier used in the determination was TEFV made by Powdertech Co. An amount of electrification of a toner which was prepared without adding the Bontron N-03 in the manufacturing process was determined in the same manner to be 4 µC/g with 5 minutes agitation. The difference of the amount of electrification in the case added with Bontron N-03 and the other case which did not use Bontron N-03 was 23 µC/g. FIG. 3 indicates a schematic illustration of an imaging apparatus using the toner prepared by the method of the present invention. With using the apparatus, clear images having at least 0.5 of MTF at 600 dpi are obtainable. FIG. 4 indicates a schematic illustration of an optical system used in the above imaging apparatus. A plurality of lenses are associated with each other in the optical system, and a distance between the lenses, the numbers and kinds of the lenses are controlled corresponding to a necessary magnification. As ordinary optical microscopes are capable of magnifying an objective to 1000 times, it is possible to obtain an image having a larger magnification than that obtained by a conventional one such as a few times, or more as 10 to 1000 times. As explained above, an advantage of the present invention is to provide toner having a very narrow particle size distribution and preferable uniformity which can improve a resolution of image by making the particle size distribution of the toner narrow, and increase an amount of electrification of the toner particle to equal to or more 10 µC/g by making the shape of the particle deformed. High definition of image can be effectively controlled by using the toner obtained in accordance with the present invention.

Claims: Non-spherical electrophotographic toner particles having an average diameter d in the range of 4 to 15 µm, characterized in that (i) the volumetric fraction of the particles having a diameter d in the range of d ± 0.2 d is equal to or higher than 90 % of the total volume of the particles, and (ii) the specific surface area A (m 2 /g) determined by the BET method is in the range expressed by the equation 7/(D·d) ≤ A ≤ 10/(D·d), wherein D is the density of the particles (g/cm 3 ). Toner particles according to claim 1, characterized in that the particles have surface irregularities of atmost 2 µm in depth. Toner particles according to claim 1 or 2, characterized in that the particles have a ratio (a)/(b) which is less than 2 where (a) is the major axis and (b) is the minor axis of the toner particles, respectively. Toner particles according to any of claims 1 to 3, characterized in that the particles have an electrical chargeability of at least 10 µC/g. Toner particles according to any of claims 1 to 4, characterized in that the toner particles are polymerized toner particles. Toner particles according to any of claims 1 to 5, characterized in that the volumetric fraction of the particles having a specific surface area A expressed by the equation 6/(D·d) ≤ A < 7/(D·d) is equal to or less than 10 % of the total volume of the particles. Toner particles according to any of claims 1 to 6, characterized in that the toner particles are made of a polymer obtained by a polymerization of at least one kind of monomers having at least an ester group. Toner particles claimed in claim 7, wherein the monomer having at least an ester group is selected from alkyl acrylates and alkyl methacrylates. A method for manufacturing the non-spherical electrophotographic toner particles according to any of claims 1 to 8, comprising the steps of: (a) providing polymerized toner particles comprising monomer units having a hydrolyzable group, (b) aggregating the particles in the polymerization system through hydrolysis by making the system alkaline, (c) separating the aggregates of the particles from the reaction system, (d) disintegrating the aggregates of the particles by acidifying the system, and (e) collecting the resulting toner particles. The method according to claim 9, characterized in that particles made of a polymer comprising monomer units having an ester group are used in step (a). The method according to claim 9 or 10, characterized in that particles made of a polymer comprising monomer units having an amido group or an imido group are used in step (a). The method according to any of claims 9 to 11, characterized in that particles made of a polymer comprising at least one kind of monomer units selected from alkyl acrylates, alkyl methacrylates and vinyl acetate are used in step (a). The method according to any of claims 9 to 12, characterized in that alkali metal hydroxides, alkaline earth metal hydroxides and/or ammonia are used in step (b) for making the system alkaline. The method according to any of claims 9 to 13, characterized in that the disintegration of the aggregates in step (d) is performed by dispersing the aggregates in an acidic solution. Use of toner particles in an electrophotographic, developing apparatus for forming toner images characterized in that said toner particles are the toner particles as claimed in any of claims 1 to 8. Use of toner particles in an electrophotographic developing apparatus according to claim 15, based on two-component toner image formation, said toner particles being used with a carrier.

Inventors: IWASAKI KISHIRO, MURAO KENJI, SASAKI HIROSHI, IWASAKI, KISHIRO, MURAO, KENJI, SASAKI, HIROSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1994
Main classification: G03G9
IPC codes: G03G9, G03G15, G03G13